GB2103800A

GB2103800A - Measuring instrument

Info

Publication number: GB2103800A
Application number: GB08222124A
Authority: GB
Inventors: William Robert Owen Harris; David Percival Harris
Original assignee: WHITEBARN IND Ltd
Current assignee: WHITEBARN IND Ltd
Priority date: 1981-08-05
Filing date: 1982-07-30
Publication date: 1983-02-23
Also published as: GB2103800B

Abstract

A measuring instrument (10) for determining the diameter of a cylindrical object (15) comprises a pair of arms (12) having a predetermined, possibly adjustable, included angle (2 phi ) therebetween and which contact the object (15) tangentially. A probe (13) which is movable relative to the arms (12) along the bisector of the angle (2 phi ) contacts the object (15) and the distance between the end (18) of the probe (13) in contact with the object (15) and the apex (17) of the angle (2 phi ) between the arms (12) is determined by a scale or by means of a transducer (14) which produces an electrical signal to be fed to a digital readout or to a calculator for determining the radius of the object (15) directly. In an alternative embodiment the arms (12) and probe (13) are replaced by light beams which touch the surface of the object tangentially at the cut-off limit. <IMAGE>

Description

SPECIFICATION Measuring instrument This invention relates to measuring instruments, and in particular to instruments for measuring the diameter of cylindrical objects and workpieces.

It is a particular object of the present invention to provide an instrument which may be used to measure the diameter of large objects or those to which access is difficult. In such cases it may be difficult or even impossible to use calipers, a micrometer or other known measuring instrument which requires access to the cylindrical object at each end of a diameter. It is also an object of the present invention to provide an instrument by means of which the degree of roundness of an object, the depth of a surface indentation, or the axial profile of an object, may be measured accurately.

The invention provides a measuring instrument for determining the diameter of a cylindrical object comprising means defining two tangents to the surface of said object from a first point spaced therefrom, said tangents having a predetermined included angle therebetween, means for locating a second point on said surface and on the bisector of said angle, and means for determining the distance between said first and second points.

The determining means may include calculating means adapted to calculate the radius of the object from values of said angle and said determined distance. The angle may be adjustable.

The defining means may comprise a radiation transmitter adapted to transmit two beams of radiation in directions having said included angle therebetween, and for each of said beams a radiation receiving means positioned relative to said transmitter to receive said beam. The locating means comprise a second radiation transmitter positioned on one side of the bisector of said included angle and adapted to transmit a third beam of radiation in the plane containing said two beams and in a direction transverse to said bisector, and a third radiation receiving means positioned to receive said third beam at that side of said bisector opposed to said one side. The second transmitter means and the third receiving means may be constrained to move in unison in directions parallel with said bisector.

The second transmitter may be connected to a transducer adapted to produce an electrical signal dependent upon the position of the second transmitter relative to the first transmitter. The radiation may be visible light.

Alternatively, the defining means may comprise a pair of arms disposed having said included angle therebetween. The locating means may comprise an elongate probe member mounted relative to said arms and constrained to move along an axis lying in the plane of said arms and bisecting said angle.

The instrument may comprise a body having said arms integral therewith and extending therefrom, said probe member being movably mounted in said body. Alternatively said arms may be mounted on said body so as to be pivotally adjustable relative thereto, whereby said angle may be adjusted.

The determining means may comprise a scale provided on one of the probe member and the body, and a pointer or marking provided on the other adjacent the scale. The probe member and the body may be relative slidable, or alternatively the probe member and the body may have cooperable screw threads thereon, in which cases said scale may comprise a vernier or micrometer scale, respectively.

As a further and preferred alternative a transducer may be provided to which said probe member is connected, said transducer being adapted to produce an electrical signal which is dependent upon the position of said probe member relative to said arms and which may be used as the input to digital readout means, moving pen and chart indicating means or a visual display unit.

The invention will now be described with reference to the accompanying drawings in which Fig. 1 is a diagrammatic elevation of one embodiment, Fig. 2 is a diagrammatic elevation of a second embodiment, and Fig. 3 is a diagrammatic elevation of a third embodiment.

Referring now to Fig. 1 there is shown a measuring instrument 10 comprising a body 11 and a pair of arms 12 integral therewith. A probe member 13 is slidably mounted in the body 11 and is connected to a transducer 14 mounted on the body 11.

In order to measure the diameter of a cylindrical object 1 5 the instrument 10 is placed against the object 1 5 with the inner sides 1 6 of the arms 12 in contact with object 1 5 as shown in Fig. 1. The arms 12 are disposed so that their inner sides 1 6 have a predetermined angle therebetween, represented by 20 in Fig. 1, and the probe member 1 3 extends and is movable along the bisector of angle 20 passing through the apex 1 7 of angle 20. The probe member 13 is moved so that its free end 18 is in contact with the object 1 5.

If R is the radius of the cylindrical object 1 5, and d is the distance between the apex 1 7 and the free end 18 of probe member 13, then it can be shown that R=dSin0/1 -SinO. The transducer 14 is arranged so that its electrical output is proportional to the longitudinal movement of probe members 13, i.e. proportional to the distance d, and hence the radius of the object 1 5 may be readily determined.The electrical signal from transducer 14 may be used as the input to an instrument (not shown) directly indicating the dimension d, or alternatively such signal may be used as the input to computing and indicating means (not shown) which indicates the radius, or diameter, of object 1 5 in accordunce with the above relationship between, R d and 0. In either case the indicator means may comprise a digital readout, visual display, or moving pen and chart device.

By means of instrument 10 the diameter of a cylindrical object 15, in particular a large object or an object to which access to diametrically opposite points is difficult or impossible, may be measured. If the instrument 10 can be moved around the periphery of object 1 5 or object 1 5 can be rotated about its axis the true roundness of the object 1 5 may be determined. Also the depth of relatively small surface indentations may be determined by comparison between the readings given by the instrument 10 when the probe 13 is in contact with the bottom of the indentation and with the unindented periphery of object 1 5.

Furthermore if the instrument 10 is moved parallel with the axis of the object 1 5 an indication of the profile of the object 1 5 may be obtained. This is of particular application in the context of cylindrical rolls as used in steel mills which are required to be of barrel shape, i.e.

possess a slight taper towards each end. Such rolls are referred to as cambered and the shape of the camber may be determined in this manner.

Furthermore, in the context of steel mill rolls, such rolls require frequent machining. The electrical signal from the transducer 14 of instrument 10 may therefore be used to monitor or control the turning machine for machining such rolls in a manner conventionai in the machine tool control art.

As an alternative to transducer 14, particularly if a less expensive and/or less accurate instrument is required, a simple pointer and scale may be provided, and such scale may be a simple scale indicating the dimension d or calibrated so as to indicate the radius R or the diameter of object 1 5.

If greater accuracy is required, than such a simple scale provides then a vernier scale may be provided, for example a micrometer scale. In the latter case the probe member 1 3 is mounted in body 11 by means of cooperating screw threads thereon.

Referring now to Fig. 2 there is shown an instrument 20 of which the parts corresponding with those of instrument 10 are given corresponding identifying numerals. In the case of instrument 20 however the arms 12 are pivotally mounted on body 11 about a common pivot axis 21. The angle 20 between the inner sides 16 of arms 12 may be varied as desired by turning nut 22 to which two rods 23 having oppositely handed screw threads are secured. Nut 22 is retained in the axis of the instrument 10 by means of arms 23 secured to body 11 or integral therewith.A pointer or mark (not shown) on an arm 1 2 may move relative to a scale (not shown) on the body 11 so as to indicate the value of the angle (3, and transducer or scale 14 indicate the dimension d, so that the radius R may be calculated in accordance with the aforementioned relationship therebetween. Alternatively a second transducer (not shown) may be provided which is adapted to provide an electrical signal proportional to angle 0, such signal being fed, together with a signal from transducer 14, to a computing and indicating device which indicates directly the value of radius R or the diameter of object 1 5. Such indication may be in any of the forms referred to in relation to instrument 10.

Other constructions of arm pivoting means will be readily apparent to persons skilled in the art, for example sliding or rotating cam arrangements, and such constructions are considered to be within the scope of the present invention.

Referring now to Fig. 3 there is shown a measuring instrument 30 which comprises two light transmitters 31,32 and three light sensors or receivers 33, 34 and 35. The transmitter 31 emits two narrow light beams 36, 37 which are at a predetermined angle 20 relative to each other and light sensors 33 and 34 are positioned so as to receive light beams 36 and 37 respectively.

Such an arrangement may be fixed or may be adjustable as desired, being equivalent to the mechanical devices of the first and second embodiments described herein. The arrangement of the transmitter 31 and sensors 33, 34 and the object 38 whose diameter is to be measured are moved relative to each other until they are positioned as shown in Fig. 3 at the limit of the sensing by sensors 33 and 34 of light beams 36, 37. In such a position a line R along a radius of the object 38 must pass through the transmitter 31 and bisect the angle 20 made by the light beams 36, 37. The transmitter 32 and sensor 35 are arranged to transmit and receive a narrow light beam 39 which is transverse to the aforementioned angle bisector R. The transmitter 32 and sensor 35 are movable in unison in a direction parallel with the bisector R and are moved towards the object 38 to the limit, as shown in Fig. 3, at which the light beam 39 can be sensed by sensor 35. The distance d is then measured using a transducer and a movable probe or arm connected thereto and to the transducer as described in relation to embodiments 1 and 2. The radius of the object 38 is then determined from the dimension d and the angle ? as in the previous embodiments.

Although light is preferred owing to the simplicity and cost of the transmitting and receiving devices other forms of radiation, for example infra red, ultra-violet or sonic radiation, may be used if desired.

Claims

1. A measuring instrument for determining the diameter of a cylindrical object, comprising means defining two tangents to the surface of said object from a first point spaced therefrom, said tangents having a predetermined included angle therebetween, means for locating a second point on said surface and on the bisector of said angle, and means for determining the distance between said first and second points.

2. An instrument according to claim 1 wherein said determining means includes calculating means adapted to calculate the radius of said object from values of said angle and said determined distance.

3. An instrument according to claim 1 or claim 2 wherein said angle is adjustable.

4. An instrument according to any one of claims 1 to 3 wherein said defining means comprises a radiation transmitter adapted to transmit two beams of radiation in directions having said included angle therebetween, and for each of said beams a radiation receiving means positioned relative to said transmitter to receive said beam.

5. An instrument according to claim 4 wherein said locating means comprises a second radiation transmitter positioned on one side of the bisector of said included angle and adapted to transmit a third beam of radiation in the plane containing said two beams and in a direction transverse to said bisector, and a third radiation receiving means positioned to receive said third beam at that side of said bisector opposed to said one side.

6. An instrument according to claim 5 wherein said second transmitter and said third receiving means are constrained to move in unison in directions parallel with said bisector.

7. An instrument according to claim 6 comprising a transducer to which said second transmitter is connected and which is adapted to produce an electrical signal dependent upon the position of said second transmitter relative to said first transmitter.

8. An instrument according to any one of claims 4 to 7 wherein said radiation is visible light radiation.

9. An instrument according to any one of claims 1 to 3 wherein said defining means comprises a pair of arms disposed having said included angle therebetween.

10. An instrument according to claim 9 wherein said locating means comprises an elongate probe member mounted relative to said arms and constrained to move along an axis lying in the plane of said arms and bisecting said angle.

11. An instrument according to claim 10 comprising a body having said arms integral therewith and extending therefrom, said probe member being movably mounted in said body.

12. An instrument according to claim 10 comprising a body, said arms being mounted on said body so as to be pivotally adjustable relative thereto whereby said angle may be adjusted.

1 3. An instrument according to claim 11 or claim 12 wherein said determining means comprises a scale provided on one of said probe member and said body and indicator means provided on the other adjacent said scale.

14. An instrument according to claim 13 wherein said probe member and said body are relatively slidable.

1 5. An instrument according to claim 14 wherein said scale and indicator means comprise a vernier scale.

1 6. An instrument according to claim 13 wherein said probe member and said body have cooperable screw threads thereon.

1 7. An instrument according to claim 16 wherein said scale and indicator means comprise a micrometer scale.

18. An instrument according to any one of claims 10 to 12 comprising a transducer to which said probe member is connected and which is adapted to produce an electrical signal dependent upon the position of said probe member relative to said arms.

19. An instrument according to claim 7 or claim 1 8 comprising digital readout means adapted to receive said electrical signal and to display a distance reading dependent thereon.

20. A measuring instrument for determining the diameter of a cylindrical object substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.